Anyone walking around the outer green belt, Takufeld or town forest after dark these days is likely to see them: tiny points of light floating between the trees, others glowing on the ground. It’s firefly season. And it has just reached its peak.
“It’s high season,” says Cologne geologist and naturalist Sven von Loga, who has been offering night firefly excursions in Zollstock and Frechen-Königsdorf for many years. Fireflies usually fly about two weeks later, around June 24; Exactly when and for how long always depends on the weather, says Loga. “Fireflies really like warm weather like this. Plus it rained a lot last weekend, so it’s not too dry.”
Warm weather is ideal for fireflies, but drought is dangerous
Adult fireflies become visible only for a short period, about two weeks. They glow to mate: the most common species in Cologne, the small firefly, has glowing males that fly in the dark. Females sit on the ground and send out their own light signal. If the male finds a glowing female, mating occurs. The female then lays anywhere from a few dozen to more than 100 eggs, after which the adult fireflies die. After a few weeks, the larvae hatch and then live hidden in leaves and dead wood for two to three years.
The environmental education center Gut Leidenhausen in Cologne-Porz also offers firefly excursions, although the last dates will be June 26 and 27. “The interest is overwhelming—this is one of our best tours ever, with long waiting lists,” says Robert Shallin, a biologist and managing director of the environmental education center.
I think we have significantly more fireflies than usual this year.
Robert Schallin, Gut Leidenhausen Center for Environmental Education
He’s noticed something special this season: “I think we have a lot more fireflies than usual this year,” Shallin says. “I would put it down to the fact that last year was also very good for snails because of the rain – and they are eating the larvae.” Drought is dangerous for fireflies because the larvae themselves can dry out, but this also jeopardizes their nutrition. If it rains often enough, the rule for fireflies in the summer is that the warmer the better. “Last week was amazing—you could actually see hundreds of people there,” Shallin enthused.
However, during his excursions he always notices how many people have never seen a firefly: “Often at least half the people.” And this despite the fact that the animals are not rare. In parks or forests it is now difficult to pass by them after dark, “but where there is light, the fireflies practically disappear.” And this is what happens in cities in most places.
Too much light disrupts mating behavior in animals.
According to Sven von Logue, light pollution is one of the biggest problems for fireflies. “If it’s too bright, the males won’t be able to find the females,” he explains. Even street lights, garden lights or car headlights can disrupt the animals’ orientation. Even a flashlight has an effect: “When I turn on the light in the forest, they turn off their light first.”
The city of Cologne is also concerned about firefly protection. During firefly mapping, citizens reported more than 1,000 sightings. The resulting map shows phenomena predominantly in the outer green belt, but also in the inner green belt and many other parks. The city of Cologne notes that despite numerous reports, the animals still depend on suitable, darkest possible habitats.
If you have your own garden, you can do something about the firefly population. Von Loga recommends not keeping the garden too tidy and, if possible, avoiding lighting the garden at night. “You should just leave the dead wood and leaves and piles of branches lying around so it can modernize a little.” There, not only firefly larvae find shelter, but also their favorite food: snails and other small animals.